Perception and the External World 1

 Direct Realism is the doctrine that perception puts us in direct contact with reality.  “Direct” because nothing comes between the world and our perception of it.  “Realism” because there is an external world that is not affected by our thoughts. 2

1. What we see is bent. 2. The pencil is not bent. 3. So what we see is not the pencil. 3

 Sense data are the objects that are immediately known in sensation, such as colors, sounds, smells, hardnesses, roughnesses, etc. 4

 We can’t compare our sense data with the world; all we can do is get more sense data.  So how can we know what the world is like in itself? 5

 Representative realism is the doctrine that sensations are caused by external objects and that our sensations represent those objects. 6

 Locke believes that the hypothesis of an external world provides the best explanation of our sense data.  Compare that hypothesis with the dream hypothesis. Which does better with regard to the criteria of adequacy: simplicity, scope, conservatism, and fruitfulness? 7

 A primary quality is one possessed by material objects such as: solidity, extension, figure, and mobility.  A secondary quality is one that exists in the mind but not in material objects themselves such as: heat, color, taste, etc.  According to Locke, sense data of primary qualities resemble the qualities of material objects. 8

 Primary qualities such as figure and extension are as variable as secondary qualities.  What looks round from one angle can look elliptical from another.  Consequently, they can’t be considered to resemble qualities of physical objects. 9

 Material objects are supposed to exist even when no one is thinking about (conceiving of) them.  Berkeley claims that material objects cannot exist because it’s impossible to conceive of something that exists unconceived. (Once you conceive of it, it’s no longer unconceived!) 10

 Since one cannot conceive of something existing unconceived, Berkeley concludes that it’s impossible for something to exist unconceived.  Thus, everything that exists must be conceived by someone. 11

 If to be is to be perceived, it would seem that when we stop perceiving something it ceases to exist.  But although we may stop perceiving something, God never stops perceiving anything.  So God holds things in existence by thinking about them. 12

There once was a young man who said “God Must think it exceedingly odd If he finds that this tree Continues to be When there’s no one about in the quad” 13

Dear Sir: Your astonishment’s odd I am always about in the quad And that’s why the tree Will continue to be Since observe by Yours faithfully, God 14

 Berkeley held that things are nothing but patterns of sensations.  According to phenomenalism, all talk of things is reducible to talk of sensations.  Objection: What we perceive depends on the state of our bodies, but the state of our bodies cannot be reduced to sensations. 15

 It is not possible to conceive of something that exists unconceived.  But it is possible to conceive that something exists unconceived.  Thus the notion of material objects is not self-contradictory. 16